Deputy Environment Minister Wu Xiaoqing has urged caution amid a big dam-building frenzy on the upper reaches of the Yangtze River, saying the lessons of past dam construction in China's southwest must be learned in the face of mounting environmental concerns and resettlement controversies.

Wu's remarks, at a media briefing in Beijing yesterday marking World Environment Day, came amid heated debate on the building of four mega-dams on the lower reaches of Jinsha (Yangtze) River and the Xiaonanhai dam in Chongqing.

While supporters often tout big dams as effective solutions to poverty and the country's power shortages, critics have pointed to rampant environmental and geological hazards and simmering tensions over relocation disputes among those evicted to make way for dams.

Wu expressed concern over the building of the Xiaonanhai dam, a contentious project widely known as a pet project of Bo Xilai , the disgraced former Communist Party chief in the southwestern municipality.

Even though the Xiaonanhai dam has been mired in controversies over its devastating impact on a nearby national fishery reserve, its poor economic feasibility and Bo's heavy involvement, its preparatory work was allowed to go ahead only two weeks after Bo's downfall in late March.

'We have been closely watching the project and attached lots of attention to the opinions of the media and various social groups,' Wu said.

He said the ministry had urged local authorities to make a careful decision after thoroughly reviewing the impact of the project.

It is widely believed that once the preliminary work, costing more than 200 million yuan (HK$1.5 billion), starts, it will be virtually impossible to stop the 32 billion yuan project.

But Wu still appears to have faith in his ministry's ability to flex some environmental muscle, saying the dam project is still subject to formal approval by the environment ministry and other central government agencies.

'So far we have not received the environmental impact assessment report for the dam project,' he said.

In a broader comment on intensive dam construction along the upper reaches of the Yangtze, where as many as 36 dams are being built or planned, including the Xiaonanhai and four mega-dams on the lower Jinsha, Wu emphasised the need to learn from past lessons.

Wu, a former deputy governor of Yunnan, said that southwestern China, home to most of the big dams to be built in the coming decade, had rich environmental and bio-diversity resources and was prone to a wide range of geological risks, such as earthquakes and landslides. He said his ministry had demanded that other government agencies and local authorities carry out full reviews of the environmental impacts of existing dams before pushing for more dams, which looked poised to wreck further havoc on the environment and river systems.

'It is the prerequisite of our pursuit of active hydropower development that we should properly deal with environmental protection and resettlement,' he said.

But despite widespread public support and its elevation to full ministry status in 2008, environmentalists say Wu's ministry is still largely 'toothless' in blocking big dams built by power companies and backed by the National Development and Reform Commission.